桶排序

桶排序是计数排序的升级版。它利用了函数的映射关系，高效与否的关键就在于这个映射函数的确定

思路：

1. 根据数据规模，初始化合理桶数
2. 将数列中的数据按照桶的规模进行映射，尽量保证数据被均匀的分布到桶中
3. 每个桶使用插入排序排好子序列
4. 最后使用双指针思想使用插入排序合并每个桶，完成排序

代码实现：

#include<iostream>
#include<vector>
using namespace std;
const int BUCKET_NUM = 10;
struct ListNode {
	explicit ListNode(int i = 0) :mData(i), mNext(NULL) {}
	ListNode* mNext;
	int mData;
};
ListNode* insert(ListNode* head, int val) {
	ListNode dummyNode;
	ListNode *newNode = new ListNode(val);
	ListNode *pre, *curr;
	dummyNode.mNext = head;
	pre = &dummyNode;
	curr = head;
	while (NULL != curr && curr->mData <= val) {
		pre = curr;
		curr = curr->mNext;
	}
	newNode->mNext = curr;
	pre->mNext = newNode;
	return dummyNode.mNext;
}
ListNode* Merge(ListNode *head1, ListNode *head2) {
	ListNode dummyNode;
	ListNode *dummy = &dummyNode;
	while (NULL != head1 && NULL != head2) {
		if (head1->mData <= head2->mData) {
			dummy->mNext = head1;
			head1 = head1->mNext;
		}
		else {
			dummy->mNext = head2;
			head2 = head2->mNext;
		}
		dummy = dummy->mNext;
	}
	if (NULL != head1) dummy->mNext = head1;
	if (NULL != head2) dummy->mNext = head2;

	return dummyNode.mNext;
}
void BucketSort(int arr[], int n) {
	vector<ListNode*> buckets(BUCKET_NUM, (ListNode*)(0));
	for (int i = 0; i < n; ++i) {
		int index = arr[i] / BUCKET_NUM;
		ListNode *head = buckets.at(index);
		buckets.at(index) = insert(head, arr[i]);
	}
	ListNode *head = buckets.at(0);
	for (int i = 1; i < BUCKET_NUM; ++i) {
		head = Merge(head, buckets.at(i));
	}
	for (int i = 0; i < n; ++i) {
		arr[i] = head->mData;
		head = head->mNext;
	}
}

int main()
{
	int arr[] = { 61, 17, 29, 22, 34, 60, 72, 21, 50, 1, 62 };
	int len = (int) sizeof(arr) / sizeof(*arr);
	BucketSort(arr, len);
	for (int i = 0; i < len; i++)
		cout << arr[i] << ' ';
	cout << endl;
	return 0;
}